Kangaroos are famous for their hopping, but a slow-moving roo relies more on its tail to get around than either of its feet. The result is a what biologists call a five-limbed, i.e. "pentapedal," gait. Yes, you read that correctly. The kangaroo is a pentaped – perhaps the only one on Earth.

Researchers led by Max Donelan, Associate Professor of Biomedical Physiology & Kinesiology at Simon Fraser University, account for the Kangaroo's pentapedal status with a biomechanical analysis, the results of which appear in the latest issue of Biology Letters. Write the researchers (emphasis added):

When moving slowly, kangaroos plant their tail on the ground in sequence with their front and hind legs. To determine the tail's role in this 'pentapedal' gait, we measured the forces the tail exerts on the ground and calculated the mechanical power it generates. We found that the tail is responsible for as much propulsive force as the front and hind legs combined. It also generates almost exclusively positive mechanical power, performing as much mass-specific mechanical work as does a human leg during walking at the same speed. Kangaroos use their muscular tail to support, propel and power their pentapedal gait just like a leg.